Generator regulation



NOV. 30, 1937. R, H, KAUFMANN 2100,854

GENERATOR REGULAT ION Filed Aug. 27, 1935 VOLTS- EXCITER lfiverwtor*r Richard H.Kaufmanm His-Attorne g.

Patented Nov. 30, 1937 PATENT orncna oiammaron BEGULA'IION Biciharil n. Kaulmum, Schenectuly, N. 1r. u- II;nol'toGenera1EleotrioComm a'9mpontion o! New York Applioatlon 21, 1m, s mrm. 30,041

' 3 01 ru+zzin My invention relates to generator regulation and more particularly to automatic me'imsi'ox maintaining substantially constant voltage out put of variable speed driven dynamo-electric generators.

Most electri'cally operated devices auch as lamps, motors and appliances operate best and most efllciently at the particular voltage Ior which they are rated. The voltage o! most electric generators and particularly'direct-current generatdrs, ordinarily varies abruptly in proportion tothe speed at which they are driven and as there are many prime movers Ior generators, such as internal combustion engines, car axles, water wheels, wind mills, etc. whose speed is relatively widely variable it is clear that in such instances lt is necessary to provide voltaga regulating ineans in order to secure best operation oi! the load devices operated by the generator.

In accordance with my invention I provide a novel and simple arrangement tor securing substantiallyi constant volt'age output o1 variable speed driven dynamo-electric generators by means o! rugged vlbration-proof means making '2'5 use of the minimum riumber 01 moving parts. I

secure this result by means of an auxiliary generator driven at a speed proportional to the speed o! the main generator whose voltage is to be maintained constant and I control the excitation 30 o1 the auxiliary generator in response to the voltage of the main generator by means of a nonlinear impedance. Such a circuit ha s a number o1 advantages which will be pointed out more in detail hereinatter.

35 An object 01 my invention is to provide a novel anti simple generator regulating system.

' Another object o! my invention is to provide a rugged and inexpensive voltage control system, Ior variable speed driven generators, which em- 40 ploys a minimum number of moving parts.

A further object cf my invention is to provide a, rugged. inexpensive, simple and eilicient voltage control circuit tor variable speed-driven directcurrent generators.

4 My invention will be better understood from the following description taken in connection with the accompzznying drawing am]. its soope will be pointed out in the appended claims.

In the drawing Flg. 1 is a diagrammatic show- 50 Ing of an embodiment 01 my invention making useot opposed E. M. F.s for securing the necessary regulation, Fix. 2 is a modiflcation whereby opp0sed M. M. F.s are employed in place 015 opposed E. M. F."s-'Fiz. 3 is a modifled i'onn oi' ex- 55 citation control i!or the auxiliary generato'gp whigb niay be applied either to the circuit ot Fix. 1 or to the-circuit oi Fix. 2, Fix. 4 Is a modiflcation o! 1"Ig. 3, Fix. 5 is a iurther modiflcation of 1"ig. 3 und Fix. 6 i.s a set 015 curves ior illustrating the operation and advantases o1. my invention. II

Referring now tothe drawing and more particularly to Fig. 1, I have shown therein a main generator I which is adapted to be driven by any suitable variable speed prime mover (not shown). Generator I is shown as a direct-current macbine 10 although as i'ar as the principles 01 my invention are concerned it could also be an alternatIng-current mac hine provided suitable rectiflers were employed tor securing the riecessary excitation. Generator I is provided with a shunt fleld winding 16 2 and if desired a series winding 3 may be used to compensate io'r the efl.'ect 01 load changes. Arranged to be driven at a speed proportional to the speed 01 main generator I is an auxiliary direct-current generator 4 which, as shown, ledirect connected to the main generator by means of a shaft 5. II: is connected in series opposition with the shunt field winding 2 01 main generator I. This is indicated by the polarity symbols ior the main generator und the auxiliary generator, respectively. Auxiliary generator l i.s provided. with a fleld winding 6 whi'ch is connected to be responsive to the voltage oi the main generator I and as shown is connected across this generator. In circuit with field winding 6 is a nun-linear resistor I. 'I'his resistor has the property of reducing its resistance with increases in current therethrough or voltage applied thereto or, in other words, it has a negative current-resistance characteristlc. A preferred Iorm 01' such resistor is the ceramic resistance material disclosed and claimed in McEachron Patent 1822742 granted September 8, 1932 and assigned to the assignee of the presen t application. 'Ihat material has the trade name 'I'hyrite. 40

The operation o! the embodiment o! my invention illustrated in Fig. 1 is as tollows: II, due to an increase in speed the voltage 01 1'nain generator I increases, the current through ileld winding 6 01 the auxiliary generator 4 will also in- 4.5 crease. 'Ihis increase in excitation oi the auxiliary generator l combined with the increase in speed will produce a relatively large increase in voltage thereof and as the voltage o! the auxiliary generator l opposes the voltages 01 the main generator with respect to the fleld winding 2 the action will be to prevent an increa.se in current in the illeld winding 2 which is proportional to the increased voltage. II: can even be made to Mm the excitati on produoed by the winding-2 so as to tend to cancel the eflect o! the increased speed o! generator I on the voltage of the generator I.

The non-linear resistor I causes a. disproportionately large change in current in the field winding 6 with changes in voltage, so as to make the circuit very sensitive and provide substantially complete cancelation of the effect of changes in speed on the voltage of generator I. If the resistor I is o! the type whose resistance changes with temperature the aotion will be relatively slow. II, however, the resisto'r I is made of a material having a negative current-resistance chatacteristic without appreciable temperature dependence such as Thyrite the action Will be substantially instantaneous and will follow the exponential law RI=C wherein R is the resistance, I is the current, a is the exponent and C is a constant. By suitably choosing the exponent a and the constant C the regulating cirouit may be made extremely sensitive to very small changes in voltage oi the main generator I so that over a relatively wide speed range, such for example, 3, 4, or to l, the voltage oi the generator is held within plus or minus 2 per oent or 3 per cent o! normal.

In Fig. 2 regulation is secured by opposed M. M. F.'s instead cf by opposed E. M. F.s as in Fig. l. 'I'his is secured by means of an auxiliary opposing field winding 8 for the main generator I which field winding is oonnected across the terminals o1 auxiliary generator l. In this circuit the shunt winding 2 of main generator I is connected direetly across on the main generator I and does net: have the armature of the auxiliary generator in ciicuit therewith as in Fig. 1.

In the operation of the arrangement illustrated in Fig. 2, an increase in speed of the main generator I whioh causes an increase in voltage will in turn cause such an increase in the voltage of auxiliary generator 4 that the opposing action of auxiliary field winding 8 more than counterbalances the increase in exoitation of the field winding 2, due to the Increase in voltage, so that there is a resultant decrease in excitation of the generator I sufilcient to offset its increase in speed. Consequently only a very slight change in voltage 1s permitted. With a decrease in voltage, conesponding to a decrease in speed, the action is reversed.

In the modiflcation shown in Fig. 3 the au1dliary generator 4 is provided with an additional fleld winding 9 connected directly across the main generator I and arranged so as to oppose the fleld winding 6. In addition the fleld winding 9 is connected. across the main generator I through a. non-linear bridge circuit two of whose arms are composed of 'I'hyrite elements 1, the other two arms being composed o! conventional resistors III whose resistance values are independent cf current.

With the arrangement illustrated in Fig. 3 an extremely sensitive and accurate regulation is ohtainable as the bridge oircuit can be made very critical and sensitive to changes in voltage, while the action of the opposed field windings 6 and 9 results in an improved characteristic of voltage versus speed fox" the generator 4. The circuit shown in Fig. 3 may be used with either the circuit o1 Fig. 1 or the circuit of Fig. 2, that is to say with either opposed E. M. F.s or opposed M. M. F.s.

The operation of this arrangement may be understood more clearly from the following description. Not only are field windings 6 and, 9 in opposition to each other but as indicated on the drawing by the relative lengths of the arrows associated with each 01 these windings the normal strength of winding 6 is greater than that of winding 9. Consequently, the net ampere turns for exciting the auxiliary machine l are less than the ampere turns oi' the winding I5. II now a given percentage change in voltage of the main generator I occurs the change in ampere turns of the winding 9 will be the same percehtage laut the change in ampere turns of the winding 6 will be a much greater percentage by reason of the fach that it is energized through the neu-linear bridge circuit. Consequently the Change in net ampere turns will be due primarily to the change in ampere turns of the winding 6 and as the net ampere turns are less than the ampere turns of the winding 6 the percentage change in net ampere turns will ofdinarily be greater than-the percentage change in ampere turns of the winding 6. It will thus be seen that both the nonlinear bridge circit and the differential or opposed relation cf the windings 6 and I contribute to produce an increased sensitivity of control.

In Fig. 4 the nun-linear bridge is replaced by a simple nun-linear resistance element I while in Fig. 5 the windings 6 and 9 are connected in series instead of in parallel and the non-linear resistor I is connected in parallel with the field winding 9. With the circuit cf Fig. 5 an increased voltage causes the non-linear element to perform the double function o! inoreasing the current through the field winding 6 and at the same time reducing the proportion of the total current passing through the field winding 9.

In Fig. 6 the curve A represents the change in voltage which must be applied to the fleld winding 2 013 Fig. 1 over a given range o1 speed in order to maintain constant generator voitage. Curve Bis a curve of the change in voltage o1! the auxiliary generator l which Is necessary to produce this change in the mein fleld voltage. II: will be seen that this latter voltage is relatively low at low speeds and increases as the speed increases. For this reason a. smaller and less expensive auxiliary generator can be employed than would be the case 11 the field winding 2 were excited directly by the auxiliary machine and independently 01 the voltage o! the main generator. In other words, 115 the winding' 2 were separately excited from the auxiliary generator 4 the change in voltage o! the auxiliary machine would have to correspond to the c urve A. As this curve shows, the maximum voltage occurs at the minimum speed so that a relatively large and expensive auxiliary generator would be required for such a connection. Furthermore. the dashed lines T1 and T4 represent the range o1! minimum to maximum voltage 01 a. shunt exciter whereas the dashed lines T: and T: indicate the range 01 voltage Ior the circuit shown in Flg. 1. As will be seen, the angle between T: and T: is much less than the angle between 'I'1 and '14 thus indicating that the necessary range of control Is much less for the case where the auxiliary machine acts as an opposing or series machine rather than as a separately exciting machine.

While I have shown and desoribed particular embodiments 01 my invention it will be obvious to those skilled in the art that ohanges and modifications may be made without departing Irom my invention, and I, theretore, aim in.the appended claims to oover all such changes and modifications as fall within the true spirit and scope 01 my invention.

Wha.t I clalm as new und desire 120 secure by Letters Patent of the Unlted States, ls:

1. In combinatlon, a variable speed driven ma.ln generator havlng a, shunt-connected field windlng the current in which is substantially affected by normal changes in voltage of said generator, an auxiliary direct current generator arranged to be driven directly from seid main generator and having its armature connected in serles opposition with the shunt; fleld winding cf said main generator, a field windlng for seid auxiliary generator connected to be energized ffom across the circuit of seid main generator, und a, two-termlnal resistance element the resistance of whlch between said two terminals decreases substantially wlth increases in voltage applied between sald two terminals connected in series with the fleld winding of said auxillary generator so as to cause a percentage current change therein which is sufflclently greater than a percentage voltage change'f roduclng lt to cause the voltage cf seid main generator to be substantially independent of lts speed over a, relatively wlde range in normal operatlon.

2. In comblnatlon, a. variable speed driven maln generator havlng a. shunt connected fleld winding, means including a direct driven auxillary d1rect current generator connected to oppose the excltatlon produced by sald shunt fleld winding, a fleld windlng Ior said auxlllary generator, and a. non-linear brldge circuit having Input terminals connected across sald maln genera.tor and havlng output termlnals between different parallel palrs o! arms of sa.ld bridge between which the field wlnding of said auxlllary generator is connected.

3. In combinatlon, a variable speed driven mein generator ha.ving s. shunt connected fleld winding, a. dlrect drlven auxlliary direct current generator connected in serles opposltlon with said shunt fleld windlng, a fleld winding lor sald auxiliary generator connected to be energized from across the circuit of sald maln generator, a second fieldwlnding on seid auxillary generat'or, and a brldge circult for energlzing sald second field windlng from across seid ma.in generator so that lt opposes the flrst fleld windlng on sald auxlllary generator, at least one of the arms o! said bridge circu1t belng composed 015 an instantaneously actlng negative reslstance eurrent characterlstlc resistor.

RICHARD H. KAUFMANN. 

